The present invention relates in general to the design and construction of a load distribution apparatus for transmitting a static clamping load from a clamping device to an object. More particularly, the present invention relates to a clamping load distributor and top stop which is utilized as an intermediary for holding a fuel injector body to a cylinder head of an internal combustion engine.
Many internal combustion engines, whether compression ignition or spark ignition engines, are provided with fuel injection systems to satisfy the need for precise and reliable fuel delivery into the combustion chamber of the engine. Such precision and reliability is necessary to address the goals of increasing fuel efficiency, maximizing power output, and controlling the undesirable by-products of combustion.
A unit injector is a precision device that must meter the quantity of fuel required for each cycle of the engine and must develop the high pressure necessary to inject the fuel into the combustion chamber at the correct instant of the operating cycle. Many fuel injection units utilize a mechanical linkage from the engine, such as a push rod and rocker arm, to pressurize the fuel charge and obtain the desired fuel spray pattern. It is desirable to maintain a lubrication coating between the engaging surfaces in the mechanical linkage to reduce wear, spalling and metal fatigue. A top stop facilitates lash between the parts to enable proper lubrication therebetween. The mechanical linkage interacts with a timing plunger that is disposed within a bore formed in the fuel injector for engaging an incompressible liquid fuel. This mechanical pressurization of the liquid fuel produces an extremely high fuel injection pressure, often exceeding 20,000 p.s.i. (13,800 Newtons per square centimeter).
In the past, designers of internal combustion engines have generally used a mechanical clamping device to hold a fuel injection unit on the cylinder head. One approach is to affix a clamping device having a wishbone shaped fork at one end to the cylinder head. The clamping device is bolted to the cylinder head and the forks on the wishbone shaped end contact the top surface of the fuel injector body in two places, thereby holding the fuel injector unit in place. A second approach is to utilize a clamping plate that engages a flange formed on the outer perimeter of the fuel injector body. The clamping plate is secured to the engine by one, or a pair of bolts, thereby drawing the flange against the engine block and holding the fuel injector unit in place.
These two approaches of fastening a fuel injector unit to an internal combustion engine have a common limitation. The common limitation being that the mechanical clamping device imparts a concentrated clamping force to a portion of the fuel injector body. The concentrated clamping force distorts the bore formed in the fuel injector body thereby causing timing plunger scuffing, and ultimately the seizure of the timing plunger within the bore. Premature failure of the fuel injector unit is often attributed to the fuel injector body receiving a concentrated clamping load.
In order to try and solve, or at least minimize, the foregoing problem, designers have tried different approaches. For example, there have been a variety of load distribution devices conceived of over the years, for transferring static clamping loads produced by clamping devices. The following listing of references is believed to be representative of such earlier designs.
______________________________________ REFERENCES ______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,829,646 Cigolotti et al. May 16, 1989 4,571,161 Leblanc et al. Feb. 18, 1986 4,419,977 Hillenbrand Dec. 13, 1983 4,403,586 Taniguchi Sept. 13, 1983 3,387,867 Rogers June 11, 1968 ______________________________________ Patent No. Applicant Date ______________________________________ French No. 838,650 Fives-Lille Company March 10, 1939 ______________________________________
Even with a variety of earlier designs, there remains a need for a clamping load distributor and top stop that is easy to install and which more uniformly distributes the transmission of the concentrated clamping force to the fuel injector body, thereby reducing the distortion of the bore formed in the fuel injector body. The present invention satisfies this need in a novel and unobvious way.